Get C# value in javascript

Question

I am new to C# and want to get my C# value in javascript

I found that by doing var javacriptVariable = "<%=CsVariable%>"; it should get the value CsVariable aut of my .cs file. However when I log it it logs <%=CsVariable%> as a string

How can I get the value out m C# file?

Sounds like you are not getting the value from C# and are just assigning that as a string. How are you logging and where is your javascript e.g. inline, in its own file etc.? — majita
– majita, Commented Mar 10, 2020 at 11:05
@majita that exactly whats happening. the part i use for testing this is var javacriptVariable = "<%=this.CsVariable%>"; console.log(javacriptVariable) — Tim567
– Tim567, Commented Mar 10, 2020 at 11:10
As far as I know that is just the syntax if you are using ASP.NET Web Forms. What kind of project do you have? Is it ASP.NET at all? — Erik T.
– Erik T., Commented Mar 10, 2020 at 11:56

Dan Scott · Accepted Answer · 2020-03-10 11:48:40Z

1

The Approach I usually take is to assign the C# value to a hidden input field in which you can obtain the value data from javascript. In ASP.NET (Which it appears you are using, correct me if I am wrong) you can do something like

<asp:HiddenField runat="server" id="hdnCsVariable" />

And then in the backend .cs file on page load

hdnCsVariable.Value = "My C# Value";

And finally in the JS since ASP.NET will (usually) generate some hideous id, you can use the "ends with" selector to get your hidden input like so

console.log(document.querySelector("input[id$='hdnCsVariable']").value); // logs "My C# Value"

answered Mar 10, 2020 at 11:48

Dan Scott

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3 Comments

Adrian Over a year ago

As for your last point, it's much more reliable to use the ClientID property from the control rather than hardcoding it like you've done.. <%= hdnCsVariable.ClientID %>

Dan Scott Over a year ago

@Adriani6 is it possible to get this client id in a javascript file that does not have access to the aspx page?

Adrian Over a year ago

Yes, attach the ID as a global variable and retrieve it in other JS files. There's many ways however OP does not mention a separate JS file.

Adrian · Accepted Answer · 2020-03-10 11:59:59Z

0

While Dans solution will work, here's an alternative that I'd personally go for..

RegisterStartupScript

Example usage:

this.Page.ClientScript.RegisterStartupScript(this.GetType(), "script", string.Format("var myVariable = {0};", 123), true);

The following will render whatever you put inside the 3rd argument as a script on the page, therefore I'd put it in a PostBack or perhaps inside onPageLoad.

answered Mar 10, 2020 at 11:59

Adrian

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Comments

Hassan Saleem Ullah · Accepted Answer · 2020-03-10 12:29:04Z

0

In Asp.net you can easily use
Use Variable
protected global::System.Web.UI.WebControls.TextBox MyTextBox;
'<%= MyTextBox.ClientID %>'
Use Function
'<%=UI.ClassName.GetFunctionName%>'

answered Mar 10, 2020 at 12:29

Hassan Saleem Ullah

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